


Siren song

by Myqueenmarceline



Category: Adventure Time
Genre: Bonnie is big gay, Don't copy to another site, Dubious Science, F/F, I'm trying my best, Marine biologist Bonnibel, MerMay, MerMay 2019, Mutual Pining, Siren Marceline, Slow Burn
Language: English
Status: In-Progress
Published: 2019-05-27
Updated: 2020-02-19
Packaged: 2020-03-20 09:36:28
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 8
Words: 13,462
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18990040
Author URL: https://archiveofourown.org/users/Myqueenmarceline/pseuds/Myqueenmarceline
Summary: Bonnibel takes a summer internship and realizes that there's a lot more to the sea than what she's been studying...





	1. A surprise encounter

“You aren’t what I’m supposed to be studying.” Bonnibel said, distantly wondering if she’d finally gone insane. Sleep deprivation could cause hallucinations, but she’d actually been sleeping a little more since she’d gotten on the boat.

Marine biology was a difficult major, but her advisor had promised that this internship would be better than summer classes. Studying the strange habits of a group of Cherry Barbs down in Mexico certainly sounded better than another stifling July doing endless dissections in the non air-conditioned lab. It would also be a good chance to test out some of her designs for remotely operated subs. Such shy fish were difficult for divers to observe, so a small submarine was a much more efficient way to gather data.

The “problem” had first appeared when she’d sent Pepp_1 down. She sent it down for a good four hours while she looked over some data. Apparently, there was a very large concentration of males proportional to the females here, but the school wasn't having any of the typical issues that came with such a population. It was certainly a conundrum.

When she’d pulled Pepp back up, there was nothing on the camera. The other sensors indicated that the water was normal, it was only the video that wasn’t recording. It wasn't like her to make such a silly mistake, but it wasn't impossible…

She only began to get suspicious when it kept happening. For the past two weeks, each and every time she pulled the sub back up, the cameras had somehow been turned off. There wasn't even a switch or power button that could accidentally be pressed. Which meant that somehow, something was getting inside of the casing and disconnecting the video. It was a good thing most of the circuitry was waterproof, or Bonnibel might not have a probe to send down again.

So, she’d done the only logical thing to do: attach the cord to a powerful winch and try to catch whatever was sabotaging her hard work. This afternoon, she’d spent neatly two hours watching and waiting. When it finally appeared it was subtle; barely a tug on the cord. Hardly different from the gently bobbing motions produced by the waves, but enough for Bonnibel to notice. She hit the switch and cranked the speed up to maximum, setting the small handheld camera next to her to record as the metallic whirring continued.

Now, the evidence was right there in front of her, still clutching Pepp in its’… Hands? Fins? The appendages certainly looked more like hands. The torso would look human if not for the grey tone of the skin, but Bonnibel could see the edge of a dark tail fin swishing around in the water. The thing turned towards her, cocking its head. The eyes are dark like a shark, reflecting Bonnibel’s own wide eyes back at her.

The creature inhaled, looking around. When she spoke it was in a beautifully melodic voice, smooth and wonderful. “Do you have more fish?”

Bonnibel blinked, shaking her head a little. A sudden wave of calm washed over her, and she felt sleepy in the heat. “I tagged a few specimens earlier, but I released them back in to the water.”

She nodded, her dark hair swirling around her in the water. “All right.” She patted Pepp, placing him back up on the side of the boat. “Can you send this one down in a bit? I’m not done feeding, and it scares them.” Her words were simple, but there was a melodious quality to them that made them feel greater.

It didn’t even occur to Bonnibel to refuse. She nodded woodenly, suddenly tongue-tied. A pretty girl had never been do distracting, and if she leaned in a little she could just barely see the way the woman’s scales glimmered as she pushed away from the boat.

“Wait.” Her voice was suddenly filled with the desperation of writing an essay at 3 in the morning, and for a moment, she considered actually scrambling off the edge of the boat after her. “What’s your name?”

She giggled, and it was the most beautiful sound Bonnibel had ever heard. “Marceline.”

“I’m Bonnibel.” The words sounded so awkward, so ungraceful compared to hers. She’d never been particularly good at social interactions, but this feels even worse. The water rippled a little as Marceline moved, gliding through the water with the natural motions of someone who’d spent their entire life dancing.

Marceline nodded, and her smile revealed a mouth lined with small sharp teeth, glimmering like light bouncing off the crest of a wave. “Thanks Bonnie. See you around.”

It is only after she left that Bonnibel realized that the camera was still rolling, and she was dangerously close to falling in to the water.


	2. Another One

**Summary for the Chapter:**

> Bonnibel has a second encounter with the mysterious Marceline.

It is exactly three days, eight hours, and fourteen minutes later when their second encounter occurs. Bonnibel knew, because she’d been keeping track of it ever since she came to her senses. She would have assumed it was some kind of bizarre dream if not for the video footage.

True, it wasn’t exactly high quality, but it captured more than enough. Marceline was clearly visible when she pulled herself up out of the water, and her voice continued to have the same distinct melodic quality that had drawn Bonnibel in—albeit slightly distorted by the tape.

Every time she went over the video, she couldn't help enjoying it. It was clear Marceline’s vocal tone had some kind of hypnotic tone pitched perfectly to lull Bonnibel into a false sense of security. It reminded her unsettlingly of an anglerfish used light to draw in unsuspecting fish close enough to be eaten, but that didn't mean it worked any less.

Honestly, that wasn't the worst part of this whole fiasco. The biggest problem came when she attempted to write up some kind of report in between rounds of revising footage. The simple version of the facts sounded insane, and dressing it up in academic language wasn't much better. Was she just supposed to email her supervisors “hello, hope all is well, I found some half-human half-fish creature that may be influencing local Cherry Barbs”? They would think she'd gotten sunstroke and send someone else out to take her place.

This was weird, surreal, and bordering on insanity, but Bonnibel was certain of one thing: there was no way in hell she was passing up the opportunity to find out more. If this wasn’t some kind of mental break, it was a revolutionary find. This could put her up there with Haeckel and Darwin before she’d even finished writing her thesis.

Still, she couldn’t in good conscience send in a completely fictional report. Even if she didn't identify the cause behind it, she needed to base her observations in reality. Submitting completely falsified data was just wrong.

So, after writing down some bull about how the “observational device required maintenance”, she quickly prepped Pepp and sent him down. There were still a couple of good hours of sunlight left. She took a deep breath, listing out the genera of fish as she made sure there weren’t any knots in the cord.

It was time to focus. She couldn't get too excited about a random experience with variables she had no control over. The barbs’ strangeness might be a third variable problem, but she couldn't bring that idea up until she actually gathered useful data.

She was still leaning over the side of the boat and watching the cable unravel when she heard a faint splash. She jumped, coming perilously close to falling in as she turned around. There, dripping water on to the deck, was Marceline. She was halfway out of the water this time, her hair clinging to her shoulders and back as she hung on to the side of the boat.

“You’re still here.” She seemed mildly surprised, looking at Bonnibel the same way she might look at a particularly interesting specimen during dissection.

Despite the immense amount of effort it took to focus, Bonnibel managed to muster up a few words. “I can't just leave, I have to study the fish.”

Marceline’s smile sent a shiver down Bonnibel’s spine. Her face might have looked human, but the rows of sharp teeth hiding behind her lips most definitely weren’t. “How long does that take?”

Normally, Bonnibel was lucky when people showed interest in her work. More often than not, other people would—subtly or not—remind her that they weren't interested, and hinted she should save her facts for a lecture hall. Even if she wasn’t nearly paralyzed by Marceline’s voice, she wasn't sure it was a good idea to be very open.

“That depends on the problem. For now, I need to collect enough hours of footage to analyze—” She paused, looking to where Pepp had gone. Marceline had just asked her to be more careful about sending him down. Losing more potential footage when she was already trying to fill in gaps was not an attractive prospect.

There was a remote controller for Pepp around here somewhere. She fumbled for it, stammering out some kind of apology. Even when she wasn't directly looking at Marceline, she could still feel her presence.

“Hey, relax.” Marceline’s voice suddenly had more authority behind it. The firm tone left no room for argument, and Bonnibel nearly slumped to the ground as she dropped the water sampler in her hand. Later she was sure she would find this interesting, but in the moment, she could only stare blankly. “It’s fine. I just ate.”

“Good.” Bonnibel nodded, trying not to fidget as she watched Marceline. She’d never been particularly socially adept in the same way some of her peers were. It was even more awkward trying to think of something to say when she was literally spellbound by the being before her.

She would be lying if she said she didn't want to study Marceline, but suddenly asking incredibly invasive questions or trying to get a tissue sample seemed like a terrible idea. There were many reasons why she was pursuing biology, but one of the biggest appeals was not having to worry about consent forms. Marceline was definitely an aquatic creature, but she was also very much conscious and sentient.

“Will you tell me more about what you're studying when you have the information?” Marceline asked, sounding far more interested than Bonnibel had expected.

“I—sure.” Bonnibel’s heart was racing. This could all be a trap, but part of her couldn't help wondering if she was being genuine. In the off-chance that Marceline was as interested in humans as Bonnibel was in her species, this could be a mutually beneficial agreement.

“Good luck with everything.” Marceline smiled again, and Bonnibel found herself smiling back. “I’ll see you around.”

This time, Bonnibel managed to control the urge to go after her and watch her leave. The glimpse of the shimmering purple and black scales on her fin as Marceline dived would already keep her up all night.

**Notes for the Chapter:**

> I just wanted to give a quick thanks to everyone reading this. Things have been difficult lately, and between visiting the doctor to try and figure out what's wrong with me and navigating university course registration, I haven't had a lot of energy for writing. I still care for my other bubbline stories and will hopefully update them (and this fic) again soon. Comments and kudos really help keep me going, so thank you to everyone who takes the time to leave them.  
> I hope y'all are having a nice day.


	3. Going under

**Summary for the Chapter:**

> Bonnibel takes a dive in the name of research  
> -  
> Shoutout to nebula-gaster (on Tumblr) for beta reading!  
> Also: from this point on science jumps the shark. I'm definitely not a marine biologist, so I'm going my best approximations.

The wetsuit didn't quite fit her right, but Bonnibel supposed it was better than nothing. At least she didn't need to buy a new one with her own money. Besides, as long as she kept them rolled, the slightly baggy sleeves wouldn't do any harm. She checked her oxygen tank again, intently examining where it connected to her mouth piece to make sure everything was alright.

She’d done dives before, but never on her own. There were supposed to be other vessels in the area in case something went terribly wrong, but Bonnibel wasn’t going to put her faith in the hands of strangers. Every possible problem had been planned for. She had oxygen for four hours, even if she would probably be down for thirty minutes at the most. This part of the bay was shallow, and the Barbs weren’t particularly inclined to go any deeper. She wouldn’t even need to de-pressurize before she returned to the surface.

Besides, there was no way she could avoid this. After observing the cherry barbs’ natural behaviours in the wild, there was only one thing to do: test how they would behave in a controlled environment. She’d already prepared a fifteen gallon tank back on the boat, complete with filtered water from the bay and food for them.

The tank wasn’t large enough to hold a lot of fish at one time, but Bonnibel would be able observe the few she had closely, then tag them when she released them back in to the wild. It wasn’t ideal, but it would have to do. The resources for this project were already stretched thin enough, so all of her elaborate tank designs would have to wait for the university’s fall grants.

She took one last deep breath, then rolled over the side of the boat. Underneath the sun-warmed surface, the water was surprisingly cold. She quickly oriented herself, turning on the oxygen then strapping the tank to her back. She bobbed back and forth for a moment, and when the air flow went through uninterrupted, she began to swim deeper. The water pushed at her, but there weren’t any unexpected currents.

Soon enough, Bonnibel spotted a small group of cherry barbs. They were skittish, and even though Bonnibel swam as slowly as she could, they scattered when she got too close. Bonnibel stopped, treading water.

After a few minutes, the fish began to swim a little closer to her. Bonnibel swam forwards as slowly as she could, subtly extending the net. She opened the net, and soon had it circled around three of the fish.

Before she could try and close the net, Bonnibel distinctly felt someone tap her on the shoulder. She jumped, nearly unhooking her oxygen tube as she turned around. Marceline looked even more hypnotizingly beautiful underwater, her dark hair fanning out like a halo around her.

She moved with the natural grace of a dancer, circling around Bonnibel. If not for the curious expression on her face, it would remind unsettlingly of a shark circling a wounded fish. She reached out and took Bonnibel’s arm, examining the net.

“What’s this?” Marceline sounded different under the water. It was almost as if her voice was a living thing, electric power thrumming through the waves around Bonnibel. Despite the way the sea muffled other sounds when Bonnibel dived, Marceline’s voice remained crystal clear.

Bonnibel almost opened her mouth, but remembered she couldn't speak at the last second. She held it up for Marceline to see, then stiffly pointed at the fish. Was catching fish offensive to a mer-person? Marceline was probably preying on this group of Barbs anyways, and Bonnibel wasn’t even going to hurt the fish.

She didn't have long to spiral in to worried thoughts, because Marceline reached out and gently pulled the net from her. Marceline smiled at her and swam a little farther away, settling down on a rock. She might have seemed relaxed, but Bonnibel still hesitated to follow her.

Marceline didn’t seem to mind that. She closed her eyes, humming a little as she began to sway. Despite her distance, Bonnibel could feel the sound running through her bones.

Then, Marceline began to sing. From the moment the first note rang out through the air, Bonnibel’s thoughts began to get hazy. She felt paralyzed, barely remembering to breathe as she leaned forwards. Her voice was so beautiful, Bonnibel couldn't help being drawn towards her.

Apparently, she wasn't the only one. A small school of fish rushed past her, parting around Bonnibel and then quickly coming back together and directly swimming towards Marceline. The singing grew stronger, and Marceline held out her hand as if to usher the fish forwards.

Bonnibel continued to slant forwards, nearly tripping over her flippers as she tried to stumble towards Marceline. She frantically windmilled her arms, barely managing to balance herself and keep treading water. She felt the tune of Marceline’s voice change a little, the grip in Bonnibel’s chest loosening just enough to keep her still as she continued watching.

The fish quickly surrounded Marceline, forming a swirling red cloud around her. Marceline easily reached out and touched them, pushing a few aside and then pulling a few more of them in to the net. She moved slower than she had during their previous encounters, fluidly and effortlessly directing the fish as she wanted.

She pushed off of the rock, her singing dying back down into humming as she came closer to Bonnibel. The fish continued following her, causing her hair to swirl and glimmer with red highlights. If Bonnibel hadn't been mesmerized already, the sight of Marceline approaching her like that would have taken her breath away.

Marceline held out the bag, her humming finally dying out. Bonnibel blinked, feeling like she just woke up from an unexpected nap.

“Is this enough?” Marceline asked, wiggling the bag a little.

Bonnibel still didn't trust her voice, so she just jerkily nodded and clutched the net closer to her. The fish were beginning to wiggle around a little, twitching as if they were coming out of some form of sedation. She twisted her fingers around in the ropes, the prickling sensation confirming that this wasn't a dream.

“Good. I’ll see you around.”

With a flash of fins Marceline disappeared once again, leaving Bonnibel stunned and full of questions.


	4. Long Night

**Summary for the Chapter:**

> Bonnibel's double-duty gets her in a bind.
> 
> Shoutout to nebula-gaster (on Tumblr) for beta reading!

**Notes for the Chapter:**

> Hey y'all, I'm going away on a short vacation with family! I'll be back in a few days, but the next story update might be delayed!

In the past, Bonnibel had often been told that she took her dedication to science too far. Now, after almost 30 hours of being awake, she was beginning to wonder if they were right. Someone else might have easily been able to decide to pretend the mermaid didn’t exist, and to simply send in a report with what she had. Or, Bonnibel could go the other way and commit to saying that the mermaid is true. She had a precious few seconds of video footage that Marceline had somehow managed to miss, and all other signs pointed towards some sort of strange natural phenomenon.

Unfortunately, Bonnibel had been unable to make a decision one way or another. On the one hand, she couldn’t ignore a variable as crucial as Marceline. Even disregarding the potentially life-changing discovery of something considered a mythological creature, it was unprofessional to ignore potential influences.

On the other, the chances that anyone would believe her were doubtful at best. She would probably get booted off of this internship, maybe even completely blacklisted. On top of that, Bonnibel wasn’t arrogant enough to believe that she was the first person to encounter a mermaid. It was highly likely that, even if she was believed, her findings would somehow be suppressed. Marceline was only one mermaid, and she had immense power over Bonnibel as long as she was within earshot. There was no telling how many others were down there, and Bonnibel wasn’t about to throw herself to the sharks over one study.

Since Bonnibel had yet to make a decision, she was simultaneously working on two different reports. The sky was already beginning to get lighter again. Even as her head throbbed, she resolutely continued typing. She had to send in _something_ later today, and once that was done she could crash and nap for a day.

For now, she was working on discussing falsified footage. Thankfully, she only had to send in a couple of clips with her work. She would make up for the deficit of hours later, but sending Pepp down for almost two entire days had given her more than enough video to screenshot and turn into small video clips.

She thumbed through her notebook, mumbling numbers to herself as she punched in the temperature and salinity that had been recorded. Her headache was getting worse, and she could practically feel her neurones beginning to fire slower. Maybe she needed another caffeine boost…

She didn’t even realize that Marceline was there until she stood up to stumble to her fridge. She froze mid-stretch, staring open-mouthed at Marceline. The mermaid had been hanging from the railing for long enough to begin to dry off, but her scales still gleamed in the light on Bonnibel’s boat.

“It’s late, isn't it? Don’t you sleep?” Marceline’s voice was just as melodious as ever, and Bonnibel felt the hairs on the back of her neck stand up. The way Marceline was watching her gave her adrenaline a good kick, and Bonnibel dropped back down into her chair.

“I need to finish this.” She gestured towards her computer and the papers spread out around it, shrugging helplessly.

Instead of losing interest, Marceline only seemed more curious. “Why do you have to work on it now? What’s it about?”

Normally, Bonnibel would have enough control over herself to answer calmly and subtly get Marceline to drop the subject. Instead she leaned forwards, glaring at Marceline as she ranted. “It’s a report on the cherry barbs. You’ve made things so god-damned difficult for me. I don’t have enough video footage so I have to stretch two days into two weeks, and I still don’t even know if I’m going to send them a report that includes you or not. One report would be difficult but this much work is ridiculous and I… I’m just so tired.” She blinked, suddenly realizing that she was on the verge of tears.

She turned around, wiping her eyes as she hunched over her computer. “Sorry, I have to get back to this,” she said. She really should get back to work, but instead she just stared vacantly at her blurry screen. This was fine. She could take five minutes to cry, then get back to work.

“You’re going to send in a report about me?” Marceline was quieter, and Bonnibel winced at the note of concern in her voice.

“I don’t know.” She put her face in her hands, taking a deep breath. “I just don’t know, all right?”

Bonnibel heard a bit of splashing, and when she looked up again Marceline had moved farther along the railing. She was as close as she could get to Bonnibel, her hand gently extended. “Maybe you should sleep. Think about it in the morning.”

“I shouldn’t, I have to finish these.” Bonnibel muttered, but she couldn't even muster the energy to shake her head. Every time she blinked, she was tempted to just keep her eyes shut.

“You can wake up soon. Just close your eyes for a minute.” Marceline’s voice had taken on more authority, and Bonnibel was having trouble remembering why she was fighting this in the first place. Would it really be so bad to sleep for a little bit? She’d finished reports like this in far less time before…

“Here, I’ll help you.” Then, Marceline began to sing. It was still the most beautiful thing Bonnibel had ever heard, the sound seeming to ring out all around her and then slowly make its way inside her chest.

However, this song felt different from the previous one. Instead of drawing her towards Marceline, it made Bonnibel’s eyes feel heavy. She blinked, sluggishly mumbling something incoherent. Marceline just kept calmly singing, smiling kindly as she watched on. Bonnibel had never been able to fall asleep easily, but now, she could feel it coming.

Bonnibel barely managed to stay awake long enough to push the papers out of the way and lay her head on her desk. Marceline never left, calmly humming by her side. Between her voice and the rocking of the waves, Bonnibel was out like a light.


	5. Important Conversations

**Summary for the Chapter:**

> Bonnibel and Marceline have a proper chat.
> 
> Shoutout to nebula-gaster (on Tumblr) for beta reading!

**Notes for the Chapter:**

> Sorry for the delay on this one, I was at a convention all weekend. I also have my university orientation starting next week, and my girlfriend visiting me that weekend for some nice quality time. So I might get back to some very sporadic updates until I settle into my semester classes. I hope y'all are doing okay!

Bonnibel carefully adjusted the webcam and triple-checked her connection. The internet was always iffy this far out, and she wasn’t going to miss her meeting because her satellite wasn’t positioned correctly. She opened up Skype, hesitating for a moment before hitting the button to call. The connection loaded, the blue icon filling the screen as it began ringing. As usual, the call was answered precisely three rings in.

“Hello Bonnibel. Can you hear me?” Louisa Kagummier was one of the toughest professors at Bonnibel’s school. She simply didn't have time for students who weren’t completely dedicated to the field. Bonnibel could appreciate her passion, and the work opportunities Louisa presented her with were incredibly valuable.

Of course, part of that was reporting back to Louisa and updating her on the study’s progress. Bonnibel’s report had only gotten a rather generic positive reply from one of the professors, and a message that the other one was on vacation. Even if it wasn’t a study Louisa was working on, she could offer some valuable feedback. Bonnibel might have sent in the fake report, but perhaps she could drop enough hints to get some actual advice on how to proceed.

“Yes, I can. Can you hear me?” She asked, waving her hand a little to test if her image was loading properly.

Louisa nodded, scooting her chair forwards so she was properly sitting in her desk. “How is everything going? I appreciate being CC’d in your email, but I am not entirely certain of the significance of your findings.”

Bonnibel was tempted to make a joke about heatstroke, but Louisa probably didn't have time for it. She folded her hands in her lap, smiling nervously as she spoke. “Well, due to technical malfunctions I’ve had some trouble with observations. The footage I have seems to show the cherry barbs acting completely normal. I took a small population sample that I’m going to study. Unless there are some kind of biological factors at play, my best theory is that some sort of unusual predator migrated here, and I just haven’t had a chance to see it yet.”

Louisa nodded, jotting something down in a notebook. “That makes sense. Just be careful. Diving observations might be necessary, but if there might be an unknown predator or toxin in the water, you should proceed with caution. I lost one of my best students to a unexpected Moray.”

“Of course.” Bonnibel was already extremely wary around Marceline, although Louisa couldn't know that. “How are you doing? Are the summer labs going well?”

“Yes. Now, I actually wanted to discuss one of your semester papers. I was asked to help work on a meta-analysis of graduate students’ research methods in this field. I was interested in featuring some of your work—with a credit of course. Would you mind sharing a few drafts and writing a short summary of the methods you’ve used during your time at Ooo University?” Louisa asked, pulling out another folder and opening it.

Bonnibel would have enthusiastically gotten into a conversation about her research methods, but she heard splashing next to her. She stared in horror as two webbed hands grabbed the railing of the boat, and Marceline hauled herself up out of the water. She clutched the edge of the computer until her knuckles went white, wondering what she had done to deserve this. If there was one time that she needed to be in complete control of her tongue and mental faculties, it was when she was talking to Louisa.

“We need to talk,” Marceline said, looking more solemn than Bonnibel had ever seen her. She didn’t even try to lower her voice or be subtle.

Then, Bonnibel noted with horror that part of Marceline’s dark hair was coming into the webcam’s frame. Bonnibel frantically waved for Marceline to shut up, accidentally knocking her computer’s plug as she attempted to move it away. She fumbled with the laptop, barely avoiding dropping it.

The screen flickered, and Louisa’s voice was distorted when she called out. “Bonnibel?”

“Yes, I’m still here. Hold on a moment, the connection—” Bonnibel helplessly fumbled with her camera, covering the lens and turning to glare at Marceline.

“I need to speak to you now,” Marceline whispered, her voice chilled and firmed with power. It was an unsettling impression of Louisa, and it killed Bonnibel’s arguments before she could even begin to speak.

Bonnibel didn’t know what the problem was, but if Marceline was coming to someone who was virtually a complete stranger, then she must have been really desperate. There were a lot of things that could go wrong at sea, both for its creatures and for those who studied them. Bonnibel would never get the chance to study Marceline if she ended up leaving.

“The satellite isn’t connecting, I’m so sorry. I’ll try and call back later.” She said, typing the message into the chat at the same time.

Now, she just had to end the call. If she simply hung up, Louisa would know that Bonnibel was deliberately ignoring her. So, before Louisa could say anything else, Bonnibel force quit the application. She closed her laptop, looking up at Marceline. Whatever this was, it had better be important.

Bonnibel didn’t have the social energy to be nice, but she managed restrained herself from snapping at Marceline. “Well, what do you want?”

Marceline glanced around, then pulled herself up higher out of the water. The boat shifted alarmingly to the side as she sat down on the railing, her tail still dangling into the water below while she faced Bonnibel. Her scales shone in the sunlight, and for a moment Bonnibel simply stared at it, hypnotized.

“You said you were working on a report about me yesterday. What happened to it?” Marceline asked, still looking at Bonnibel with a strange intensity. She had seemed so relaxed when they had previously met, but today all of that playfulness had vanished.

Bonnibel blinked, trying to think for a moment. Two coffees weren’t enough to fix her sleep deprivation, and just thinking about that night made her head hurt. “Nothing. I sent in the one without you.”

“Are you lying to me?” Like a switch flipping, Marceline’s voice suddenly thrummed with power. Bonnibel couldn’t help but tell the truth.

“No. I was planning on gathering more research before I even attempted to bring you up.” She quickly closed her mouth, wondering if that was the wrong thing to say. She hadn't meant to let that much slip out, but she couldn't take it back.

Marceline sighed. She looked disappointed, but not surprised. “Bonnibel, I can’t let you do that. I don’t care about any personal research you have, but I can’t run the risk of you sharing it.”

Bonnibel couldn't help feeling a little irritated. Sure, she could understand why Marceline was acting like this, but she couldn't help feeling a little bitter. “Why not? Is it really such a big deal? This could be the greatest discovery of the 21st century. This could be a good learning experience for both of us.”

Marceline looked around, then leaned a little closer to whisper. “Listen, this isn’t just up to me. I’m not the only one down here, you know. You’d be putting all of us in danger. I’m not doing this because I hate you. The last time someone tried to spread information about us, there were over fifty people in the area the next day trying to find us. If the whole world found out that sirens really exist, do you really think they would be nice? No. We’d all be dead and dissected in a year. I get that you’re trying to do your job, but I can’t let you do this.”

A couple of years ago, someone had sent Bonnibel an article about someone finding mermaids near the Philipines. She had thought of it as an amusing joke at the time, especially since the article was written in such a serious tone. She hadn’t thought anything of it at the time, but now she couldn't help wondering if there was more to it…

All of Marceline’s points made sense, but at the same time, there was one question that still bothered Bonnibel. She looked up at Marceline, trying her best to stay calm. “Why?”

Marceline blinked in surprise, tilting her head. She used her tail to splash some water up over herself, and then leaned in again. “What do you mean?”

Bonnibel ran both hands over her face, sighing heavily. “Why even let me see you at all? Why not just destroy my research, if it’s such a threat? You’re the one who showed yourself to me! If I’m such a liability, then why on earth would you come up and see me?”

She immediately regretted the outburst. Marceline looked like she’d been struck. She turned to look at the water, swishing her tail back and forth a little.

Her response was so quiet that Bonnibel almost didn't hear it. “Because I wanted to.”

She was just digging herself deeper, wasn’t she? Bonnbiel shook her head. “I’m sorry, it’s just… Why me?” She couldn't understand. There was no reason why Marceline should pick her out of everyone.

Marceline laughed a little, shaking her head. She turned back to Bonnibel, her smile becoming a little bitter. “You don’t get it, do you? Most people who catch a glimpse of me freak out. Yeah, you were a little shocked, but you didn't let that stop you from working. You didn't try to hurt or capture me, and you talked to me even when you were annoyed. That’s pretty damn special in my book.”

“Of course I didn’t freak out about you. I’ve seen weirder.” Bonnibel didn’t know what possessed her to make the joke, but she couldn’t think of a better response.

She knew she’d made the right decision when Marceline threw her head back and laughed. Bonnibel’s breath caught in her throat at the sight, and she subtly leaned forwards in her chair. If she’d thought Marceline’s voice was hypnotizing, then her laugh was completely entrancing. It brought a smile to Bonnibel’s face, and by the time Marceline had finished giggling, Bonnibel felt a little lighter.

Marceline was still smiling when she turned back to Bonnibel, swaying a little on the railing. “How about this: let’s make a deal. I’ll tell you anything you want to know. You can study me as much as you want. But you have to promise that you’ll never tell anyone else about it. No bringing anyone else here to show them either, got it?”

“I promise,” Bonnibel said, surprised to find that she fully meant it. It was a shame that she couldn't show any of this, but at least she could document her discoveries.

Part of her also whispered that it would be wrong to break a promise like this. Marceline was far more like a person than a fish, and Bonnibel could easily see how exposing her could end badly for the both of them. After everything Marceline had done to help her, it wouldn’t be right to spit in her face by doing the one thing she’d asked Bonnibel not to.

“All right.” Marceline leaned forwards dangerously, the railing creaking a little with protest. She moved her tail a little to keep her balance, holding out a hand.

For a moment, Bonnibel didn’t understand what Marceline wanted. When Marceline wiggled her hand a little and raised her eyebrows. Bonnibel lurched to her feet as she finally realized what was happening. Marceline wanted to shake hands.

Bonnibel stepped forwards, carefully scooting so she was a little bit to the side of Marceline. It probably wouldn't be enough to overbalance the boat if she had stood directly in front of the siren, but Bonnibel didn’t want to chance falling off the boat herself. She smiled nervously, reaching out and taking Marceline’s hand.

Her hand was cooler than Bonnibel had expected, with a faintly scaly texture to it. Was her entire body made of scales, or was her skin closer to that of a shark? Bonnibel was tempted to hold it up a little higher and examine it, but she didn't want to make things awkward. Marceline had a good grip, and she vigorously shook Bonnibel’s hand. Bonnibel shook back, smiling a little. She didn't think anyone had ever been this excited to meet her.

The handshake didn’t go on for too long, and Bonnibel reluctantly let go of Marceline when the siren began to pull back. She sat back down at her desk, watching as Marceline shifted herself back into a more comfortable sitting position. She picked up one of her notebooks and a spare pen, quickly jotting down the date at the top of the page.

“I would need time to prepare some questions, but do you mind if I ask you something now?” Bonnibel asked, hoping she wasn’t being too forward. There was no starting too early on research like this, especially since she was also working on the cherry barb project.

“Go ahead.” Marceline said, relaxing against the railing.

“So, you don't have to answer this if it’s too invasive but… Why are you here specifically? Are there others with you? Is this some kind of migratory spot, or are you new to the area?” Bonnibel asked, pen poised to write down the answers. Marceline had mentioned that there were other sirens, but if that was the case, why had Bonnibel only ever seen her?

Marceline hummed, thinking for a moment before she responded. “I have a very…unique diet. I actually need to feed on fish with specific scale colours. I can’t properly digest other ones, so I have to travel and follow my food. There are a few sirens in the area but we aren’t like, a close group or anything.”

“All right.” Bonnibel nodded, quickly jotting it down. A single answer had just yielded a lot of interesting information. Not only did sirens have distinct social groups, but population variations could include mutations that resembled autoimmune diseases. Fascinating. She would have to ask more questions about Marceline’s social standing and illness later.

“Thank you,” she said, looking up at Marceline again. She grinned widely, glancing down at her notes again. She couldn’t believe that she was really going to get the chance to learn abut this.

“No problem.” Marceline smiled back at her, making Bonnibel’s heart speed up a little. Even when she wasn’t trying to influence Bonnibel, she was still strangely attractive. “Well, I should probably let you get back to that.” Marceline said, nodding towards her computer. Bonnibel winced a little, realizing that she’d left her supervisor hanging. That one wasn’t going to end well.

“Yes, I need to call her back.” Bonnibel said, shifting awkwardly. Was Marceline going to stay and watch? Bonnibel would prefer to have a private conversation, but she wasn't sure if it would be rude to tell Marceline to leave.

“Alright, see you later.” Marceline waved, then slid off the railing and into the water in one smooth, practiced motion. Bonnibel stood up, watching Marceline’s silhouette glide through the water until she disappeared. After a long moment, she turned around and opened up her laptop again.


	6. Gone Fishing

**Summary for the Chapter:**

> Bonnibel goes on a supply run, and tries to deny her feelings.
> 
> This was beta read by nebula-gaster on Tumblr, thanks buddy!

**Notes for the Chapter:**

> You ever sit there in the snow and the cold and just write a chapter of warm summer fun? Yeah, me too. Happy holidays everyone, I hope you're all having a good time! I've been visiting family for the past week, it's been nice but busy.

Of course Bonnibel would have to go on a supply run the day after Marceline had agreed to let Bonnibel study her. Unfortunately, she couldn't skip out on a supply run. The boat had a fairly limited storage space, and with all her equipment, Bonnibel couldn’t stock more than two weeks of food at a time.

It took almost four hours to get to the closest port, and it was always incredibly overcrowded. Even though she set off before dawn, she was only allowed to dock in the afternoon. Most of the supplies she bought were canned or preserved, but there was still a risk of something selling out.

Bonnibel quickly went about getting her necessities, relieved to find that her orders had properly been placed on hold. She loaded all of her water, food, and some newer nets and filtration systems as quickly as she could. The vendors had helped her load everything onto a cart, but they were too busy to come give a hand. Bonnibel understood, but it was still a little stressful. If she didn't finish early enough, the market would close and she would probably have to stay overnight.

Even if visiting the market wasn’t truly necessary, it was often useful. Bonnibel had forgotten to get saltwater-resistant cases for her computer and phone, and if she hadn’t seen that stall at the market, she might have gone out on the sea without them. Since then she made a practice of going, and every time she found something nice to take.

Thankfully, she managed to get to the market with about thirty minutes to spare. Bonnibel scanned the stands, looking for anything. She wasn't interested in the jewelry, she had all the tech, but the food… Bonnibel’s stomach growled, reminding her that she hadn’t eaten for far too many hours.

Bonnibel quickly walked up to the stands, picking out some kind of deep-fried pastry. She ate it as she walked, looking around. She easily managed to locate the stand she was looking for, quickly striding towards it.

She had met a few of the local fishermen before, but Finn seemed to have the best selection of fish on-offer, no matter the time of day. If Bonnibel remembered correctly, he had a brother who would go out on the water while he sold their wares.

Finn smiled brightly when he saw her, immediately trying to make small-talk. “Hello Bonnibel! How is the research going?”

“Oh, just fine. How’s the fishing?” Bonnibel replied absent-mindedly, focused on examining the fish. There were several good-looking options, with some very big cod and bass lined up.

“Actually, it’s been a lot better recently. I’ve been fishing a bit farther away from where I usually do, away from the spot you’re researching at. It look like you’re searching in the right area; that place has a poor yield.” Finn said, chuckling a little. “Do you have any ideas of what’s wrong with the fish over there?”

Bonnibel paused for a moment, pretending to pay special attention to one snapper. There was no way that she could tell him anything about Marceline, but she couldn't just ignore the question. “No, not yet. There doesn’t seem to be anything wrong in the water or the fish. My best guess is that there’s a… foreign predator somewhere nearby, and that it’s disrupting the area’s ecosystem.”

“Oh, that makes sense.” Finn nodded. “One time I was visiting some family and fishing at this lake way up north. It was going really poorly, but we couldn’t figure out why. A few weeks later my cousin called me and told me they’d pulled a whole shark out of the lake! No one knows how it got in there, but it had a lot inside its belly.”

“It happens more often than people realize. Bull sharks can actually survive in fresh water, and it isn’t impossible for them to get very far inland.” Bonnibel said, giving Finn a tentative smile back.

During some research beforehand, Bonnibel had found that there were a few species of shark that liked to roam this area. If Finn believed that this was simply another kind of shark, Bonnibel wouldn't work too hard to prove him wrong. After all, that could end up being her official explanation for the problem.

Bonnibel had almost decided on her order, when the glint of some scales caught the corner of her eye. The salmon was looking rather good, large and pleasantly pink. She wondered if Marceline could appreciate some of those. Even if the outside wasn’t quite the right colour, the meat inside of them was still red… Ah well. Bonnibel would just buy some of it. If Marceline couldn't eat it, then Bonnibel could always cook it up for herself.

“I’ll take one salmon, two cod, and a few of these mussels with some ice, please.” Bonnibel straightened up, reaching into her pocket.

Finn quickly wrapped up the seafood in some plastic, putting each of them into a small cooler with a good chunk of ice at the bottom. He graciously added another scoop of ice on top of the fish, ensuring they would stay nice and cold until Bonnibel got them into her fridge.

“Have a nice day! Make sure not to get too close to any sharks, they don't play around.” Finn held up his right arm, showing off a long, climbing scar.

“Thank you, I’ll be careful.” Bonnibel said, smiling a little. She wondered if any parts of Marceline had the texture of a shark’s skin. If she ever got the chance to do a more in-depth physical exam, she would have to make sure she wore gloves.

“See you around.” Finn said, waving a little.

“I’ll see you later.” Bonnibel smiled back. Finn’s enthusiasm was contagious, and he was always so kind to her.

Bonnibel made her way back to the boat, putting the fish away before heading to the bridge. She nibbled on a bit of dried fruit as she put the boat into gear. It took some maneuvering and some aggressive honking to get a tugboat to move, but she managed to get out of the port before too long.

As soon as the port was behind her, the water cleared up. Soon Bonnibel was alone on the sea, bobbing along on the waves. Her mind began to drift, and she idly tapped her fingers on the  steering wheel as she thought.

Marceline might not be able to tell her about any other sirens, but there was still plenty that Bonnibel could ask about her. For instance, did the colouring of Marceline’s scales have any particular meaning? The lighter underside made sense and mirrored other marine life, but was there a particular fish that Marceline’s colour and fins imitated? Why did she keep her hair so long? It might serve a purpose, but it also could just be aesthetics. It certainly looked beautiful, especially when it was floating underwater.

Bonnibel wondered what it would be like to touch that hair. It would definitely be wet, but it looked very soft and silky. Maybe Marceline would let Bonnibel brush it out, and braid it up into something nice. She could even put a clip in it, a heart or maybe a flower…

Wait, what was she doing? Bonnibel shook her head, tightening her grip on the controls. This was absolutely ridiculous. Bonnibel had to be an academic. She couldn't let her personal feelings complicate anything. Marceline wasn't just some girl next door to be flirted with, this was an academic study. Even if she couldn't deny Marceline’s attractiveness, Bonnibel would have to keep a tight leash on her emotions.

Before Bonnibel knew it, she was back in familiar waters. She dropped anchor, then quickly updated her log. The receipts from her latest trip got stuffed into a ziplock bag with the others, then put away in a drawer. She leaned against the desk for a moment, closing her eyes. She was tired, and her eyes longed to stay shut for just a minute more…

This was no time to rest. She’d worked longer hours in grad school. Bonnibel reluctantly stood up and made her way outside to collect her samples. Even if she hadn’t been in the area all day, missing a day of data always looked bad.

She crouched down next to the stern, leaning over to try and grab the rope holding her tools. After a few attempts she managed to snag it, reeling it back up. She carefully unhooked her thermometer and the small test tube of seawater she had collected, noting down the temperature. She opened the test tube, and was about to put some of the water into the refractometer when it happened.

“You left very suddenly this morning.” Marceline’s came from behind Bonnibel, making her nearly jump out of her skin.

Bonnibel whirled around, staring at the siren with wide eyes. Marceline had somehow managed to climb up onto the railing without making a single splash. She was dripping water onto the deck, but Bonnibel’s main concern was how alarmingly close she was. If she hadn’t said anything, Bonnibel never would have noticed she was there. She was tapping her claws against the railing now, seemingly unaware of Bonnibel’s sudden spike in blood pressure.

“Yes, well, hello to you too.” Bonnibel said lamely, quickly turning back to her notebook. She could feel the weight of Marceline’s gaze, but she was too anxious to look up. She couldn't let herself be caught off-guard like that if she wanted to keep this professional.

“Where were you?” Marceline dropped back into the water with a splash, her tail fin curling tantalizingly just over the edge of the boat as she swam her way around.

Bonnibel sat down and crossed her legs, resigned to having this conversation. She tucked her notebook away in her pocket, waiting until Marceline’s head popped up on the edge of the boat near hers to speak. She tried not to notice the way water rolled down Marceline’s pearly skin, or the way her plump lips glistened a little.

She cleared her throat, forcing herself to focus on the facts. “It’s been a few weeks since I had to make a supply run, and I had to go back into town for some fresh water and food. The trip takes awhile, so I left as soon as I felt comfortable navigating. In the past I’ve actually had to dock overnight to avoid traveling on rough waters… Why does any of this matter to you? You don’t spend most of your time on the boat, or even near the fish.” Bonnibel knew that she was being unpleasant, but she couldn't help it. She was tired and full of confusing feelings, and all she wanted to do was rest.

Marceline looked down, and for a moment Bonnibel thought she was just going to leave. When she spoke, it was so quiet that Bonnibel could barely hear it. “I was worried you were leaving for good.” The sadness in her voice made Bonnibel’s chest ache, but it was the resigned tone that really got to her. It seemed like Marceline had been betrayed before, and she wasn't surprised that Bonnibel would do the same.

Bonnibel unthinkingly reached forward, putting one hand on Marceline’s head. Her hair felt slick, the texture more like thin strands of seaweed than Bonnibel’s hair. She tried to ignore the urge to study it, instead gently patting her head. “I made a promise, didn’t I?” Bonnibel asked, smiling a little.

She quickly pulled her hand back, waiting to see if she’d done something wrong. She’d never been the best at consoling people, and she couldn't tell what the look on Marceline’s face meant. Maybe it would be best to just move on, and act like things were fine.

“Speaking of that, I bought you something. Here, let me go get it.” Bonnibel said, standing up and practically fleeing back to the cabin.

Bonnibel dug through the cooler, pulling out the salmon. Aside from being a little cold, it looked like it was fine. Bonnibel peeked through one of the windows, trying to see what Marceline was doing. She’d pulled herself up a little higher so she was sitting on the end of the boat, swishing her tail back and forth a little as she quietly waited. Bonnibel stared at her glimmering scales for a long moment before she snapped out of it, moving back to the door and walking around the boat again.

“Here.” She held out the fish, sitting down. She watched anxiously as Marceline opened up the paper, leaning in and smelling the fish.

When Marceline smiled, her lips pulled back wider than Bonnibel had ever seen them. Her teeth looked sharp, but Bonnbiel didn't feel as concerned by them any more. She couldn't be intimidated when Marceline’s eyes lit up like an excited child.

“You can’t get this kind over here.” Marceline said, glee evident in her voice. “I haven’t had it in a long time.”

“I’m glad.” Bonnibel said, returning Marceline’s smile. “I can get you even more when I do my next supply run. If you give me names or descriptions, I can even search for specific fish.”

She couldn't spend her whole budget on fish for Marceline, but Bonnibel could certainly get her a few things. Marceline seemed so excited about a single fish, and Bonnibel wanted to make her happy. She could write that off as somewhat impartial… It was essential to keep the goodwill of your test subject, after all. Plus, this would give her an idea of the range of species that Marceline could eat.

“Thank you.” Marceline moved quickly, the boat tilting to the side as she pulled herself up. Bonnibel couldn't move back quick enough, her muscles tensing in surprise as Marceline suddenly got very close.

Cold lips pressed against her cheek, and water soaked the front of Bonnibel’s shirt. Marceline stayed there for a moment, lightly nuzzling Bonnibel’s face. Her lips made a soft smacking sound as she pulled away, splashing back into the water. Bonnibel felt frozen in shock, her face heating up as she stared at Marceline.

Marceline’s smile seemed a little more mischievous, and there seemed to be a light pink flush on her cheekbones. That was probably just the light though. The kiss was merely a gesture of gratitude, and Bonnibel shouldn’t read too much into it. Her thoughts were so distracted that she almost didn’t hear Marceline speak.

“I’ll let you get back to work. See you tomorrow!” Marceline waved, and Bonnibel managed to stiffly wave back before she dove underwater.

Well, that was certainly something. Bonnibel idly began patting down her wet shirt, then gathered up her tools. She walked back inside the cabin, and sat down at her desk.

Bonnibel probably wasn’t going to be very productive, but she could at least organize her supplies. After all, she was going to have to be prepared to study Marceline tomorrow. She was _definitely_ not going to think of the kiss, or how she was going to get close to Marceline to run experiments. After all, she was a scientist. She had to remain professional.


	7. The Initial Study

**Summary for the Chapter:**

> Bonnibel finally gets the chance to study Marceline. It gets gay.

**Notes for the Chapter:**

> Shoutout to @nebula-gaster for beta reading this, I appreciate it!
> 
> I had a great time writing this chapter!. I finished this over the break, but I might need a bit longer before I can post another chapter again. In the meantime, I hope y'all enjoy this.

Somehow, Bonnibel actually managed to sleep through the night. She had some dreams she would rather not remember, but at least she was well-rested enough to know not to act on them. The sun had already risen by the time she woke up, shining directly into her eyes when she opened the window to check what the weather was like.

 

The conditions were ideal for observation, sunny and not too hot. There was a slight sea breeze, enough to make the tops of the waves a bit choppy but not enough to rock the boat. It would be foolish to waste this opportunity. Bonnibel got ready quickly, scarfing down a small breakfast and moving outside to work on preparations. She put on a lab coat, but left it open for now. It was somewhat warm outside, and sweating through her coat would probably look worse than leaving it open.

The ship’s stern was the perfect location for her studies to begin. The back of the ship’s deck had a slightly lowered square, probably meant for catch-and-release. Marceline wouldn’t fit entirely, but she could probably lie comfortably in it. Bonnibel had left a box of supplies out last night, and she quickly moved to prepare everything.

She lined two of the square’s edges with wet towels, leaving Marceline with comfortable places to rest her head and tail. It took three and a half buckets of water to fill the square. Bonnibel had also placed a mop nearby, so she would be ready to clean up the inevitable spillage. Keeping Marceline comfortable was more important than keeping the deck dry.

There were two extra buckets of sea water on standby, and of course, there was a whole body of water if Marceline could roll herself about half a metre to the right. Bonnibel had lowered the gate on the stern, leaving it open. She would probably have to pull Marceline up and out of the water, but based on the way she’d climbed up the ship and balanced on the railings earlier, Marceline knew how to stay mobile outside of water.

Bonnibel double-checked her phone, still open on the voice recorder app she’d installed last night. She had a long list of questions to ask, and it would be far more convenient if she could simply record their conversation and transcribe the answers later. She could also back up the file onto her computer, thus ensuring that she had multiple copies of the interview.

Everything seemed as ready as it could be. Bonnibel was ready to accommodate Marceline’s needs, and flexible to change. All she really wanted was a starting idea of Marceline’s biology, and some samples to take for later.

She heard a splash and opened her eyes, not even realizing that she’d sat down. She quickly jumped up, walking over to the stern where Marceline was holding on to the side of the boat. It was clear what the problem was: the back of the boat was too high for Marceline to pull her whole body on to.

Marceline looked up at Bonnibel, holding out a hand. “Hey, do you mind? I just need a quick boost, I can get to the pool by myself.”

“Of course.” Bonnibel grabbed Marceline’s hand, grunting as she pulled hard. She hoisted Marceline up as much as she could, making sure to lift with her legs. During one internship she’d had to carry around 50-pound boxes of files before, so it wasn't too difficult.

She dragged Marceline about thirty centimetres forwards before Marceline pulled away, flopping down on the deck. Bonnibel stepped forwards, but Marceline waved her off with a curt ‘I’ve got this’. Bonnibel stepped back, taking the chance to begin observing Marceline.

It was surprisingly awkward to watch Marceline move, wiggling from side to side while her tail flapped. What was even more ridiculous was that Bonnibel actually found it sort of endearing. It was funny, yes, but there was also something kind of cute about watching her struggle. Bonnibel rubbed her face, tempted to splash cold water on it to snap her out of this. She had to focus, damn it! This was only day one of research, she couldn't be acting like this already.

She watched as Marceline rolled into the divot with a splash, sighing pleasantly as she settled in. Marceline’s body was really on display now, and Bonnibel noticed that her scales weren’t the only things shining. Marceline had several golden and silvery chains on, tangled together around her neck. She didn’t have any other adornments, but Bonnibel noticed that one of the chains had a black ring with a red gemstone on it. Maybe she should ask about those once she got to the cultural section of her questionnaire.

She walked over next to Marceline, pulling up a small but sturdy crate and sitting down on it. “Alright. Before we begin, I just want to check: would you be comfortable with me recording your answers to my questions?”

“Oh, I wouldn't do that. My voice doesn't record very well.” Marceline smiled apologetically, shrugging. “You can try if you want, but you’ll probably lose all of it. There’s a reason people still can’t prove we exist.”

Bonnibel smiled, pulling a notebook and pen out of one of the pockets in her lab coat. She had stapled some sheets with numbered questions in there, so she could write down an answer without having to rewrite the entire question. “In that case, do you mind me writing down your answers and quoting you on them later?”

“Sure. Just say you got them from ‘Marceline Abadeer’, spelled like it sounds.” Marceline swished her tail back and forth, lounging back. She was watching Bonnibel, seemingly amused by her research methods.

“Excellent. Are you currently comfortable? Do you need any more water?” Bonnibel asked, giving a quick nod when Marceline shook her head. “Alright then. First question: what does your species call itself? Is there any human word which can be used to accurately describe it?”

“I’m not sure you could pronounce the name. I’ve heard humans call us sirens and mermaids, and both of those seem to be mostly accurate.” Marceline continued to move her tail idly, rippling the surface of the water without splashing it around.

“You are a fully grown adult of your species?” Bonnibel had a feeling she knew the answer, but it never hurt to make sure.

“Yes.” Marceline was definitely amused now, giving Bonnibel a smile that made her quickly look back down to the paper.

“That’s good. Er, this next part might be a bit awkward… Do you mind if I take some measurements? All for my records, of course,” Bonnibel said, wondering if Marceline would somehow be able to not notice her blush.

“Sure thing. Just tell me what you need.” Marceline stretched, putting her arms above her head and smirking at Bonnibel.

Bonnibel looked away, opening up her supply box and pulling out a tape measurer. She pulled some of it out, and it seemed to be working just fine. She stood up, leaning down to give one end to Marceline.

“Hold this up here by your head.” Bonnibel handed Marceline the end of the tape measurer, watching as Marceline held it up. She touched Marceline’s wrist for a moment, moving her hand so it was right at the top of her head.

“Just stay still for a moment.” Bonnibel stepped backwards, being careful not to slip in a puddle.

Officially she was supposed to be making sure the tape measurer was close to Marceline’s body and didn't somehow get tangled, but Bonnibel couldn’t help staring. Marceline was a little uncanny; she looked so human in some ways and so alien in many more. She was definitely alluring, and Bonnibel wondered if the fact that she was still attracted to the siren said anything about her.

The tape measure clicked warningly, and Bonnibel realized she’d overshot Marceline’s tail fin by a few centimetres. She hesitantly laid one hand on the webbed flesh, slowly moving the tape back. She squinted, double-checking to make sure that she’d gotten the measurement right. She pressed the tip of the measurer against Marceline’s tail, but the result didn’t change.

From head to tail, Marceline was 219.5 centimetres. Not as long as Bonnibel had first imagined her to be, but certainly taller than her own 179.4 centimetres. Marceline seemed far leaner than Bonnibel was, her body almost all muscle. Bonnibel didn’t have the hydraulics to make a proper lifting rig, but she could estimate that Marceline probably weighed around 200 pounds.

Bonnibel stood up, walking back over to Marceline. Once she was just under half a metre away she tilted the measuring tape up higher, clicking the button and making the tape automatically retract back into the box. Marceline looked at the device in surprise, perking up in interest.

“Can I hold that for a minute?” Marceline asked, holding out her hand like a child who’d just seen a new toy.

“Sure, but don’t let it hit you.” Bonnibel handed the measuring tape over, feeling Marceline’s fingers brush against hers. She glanced down at her notebook again, wondering if she should just proceed in order.

“Actually, I was also hoping for some other samples, if they weren’t too invasive.” Bonnibel clicked her pen, twisting it around between her fingers. “Specifically, it would be nice to have a scale or two so I could analyze the composition and form of them, and also a few hairs from your head. Do I have your permission to take those samples?”

“You want a saliva swab too?” Marceline was looking at her with a smug smirk again, like she knew exactly what she was doing. She pulled some of the tape out, letting it snap right back into place as she stared at Bonnibel.

“I—no, I don’t think that will be necessary.” Bonnibel began rummaging through her supplies box, keenly avoiding Marceline’s gaze.

It was a good thing she’d gathered all of her essentials up beforehand; she was feeling scatterbrained enough just trying to get what she needed from a single box. Bonnibel pulled out her first aid kit, taking out a sealed and sterilized pair of tweezers. She also grabbed a few small sealable plastic bags, and a box of disposable rubber gloves. They weren’t very high quality, but as long as there weren’t any rips they should serve their purpose.

Bonnibel went and knelt next to Marceline, carefully pulling on a pair of gloves. She looked over Marceline’s tail, trying to find a good place to take from. The scales all seemed to mold together into one shiny surface, and even up close, Bonnibel could see that they were very carefully interlocked. If she pulled one out, she could potentially expose Marceline to infection. She frowned, wondering if there was a non-awkward way to bring this up.

Marceline tapped her right hip, turning it bit towards Bonnibel. There was a small ridge rising there, a slight disturbance in the sleek surface. “Pull from this part, there are a few extra scales.”

Bonnibel had to lean over to get to the area, planting her knees right in a puddle. She was focused on that, not on how perilously close she was to Marceline. She examined the area, tentatively brushing one finger over the ridge of scales. Right near where it ended, several scales seemed to have grown haphazardly on top of each other.

She held the tweezers carefully between her thumb and forefinger, taking one and gently pulling it. She tried to go slowly, but since Marceline didn't seem to react at all Bonnibel tugged with a little more force. The scale came off fairly easily, clicking softly as it brushed against its brethren. Bonnibel opened the plastic bag with one hand, carefully putting the scale in.

For a moment, she managed to completely focus on the task. She quickly pulled out two more scales, putting them each in their own individual bags. She pressed her fingers against the raised area, lightly palpating it to see if there was any irritation or swelling. The tissue seemed fine, the scales over it still properly attached. Bonnibel leaned in closer, examining the way the pattern seemed to curve over the muscle of the tail.

She looked up again when Marceline chuckled softly, her face heating up as she realized how close she was to Marceline’s chest. For someone who was half fish, she definitely had some more… humanlike attributes. Marceline was wearing part of a shirt, but there was still a fair bit on display.

The mermaid had both of her arms above her head, sticking her hip out even more as she posed for Bonnibel. “You want a picture or something?”

“I—um, yes, a picture could actually be good documentation, but let me finish this first.” Bonnibel moved away from Marceline, awkwardly shuffling towards Marceline’s head on her knees. “Please sit up.”

“Do you have to use the gloves on my face?” Marceline almost seemed disappointed, but she pushed herself up onto her elbows anyways.

Bonnibel didn’t want to make Marceline uncomfortable, but she wasn’t about to abandon the scientific method. She looked at her hands, sighing. “I suppose I could take this one off, but I don’t want to contaminate the sample. Does that work?”

“Sure.” Marceline smiled at Bonnibel, closing her eyes.

“Alright, please stay still.” Bonnibel pulled the glove off her right hand, turning Marceline’s face a little more towards her.

Bonnibel realized that it might be weird that she’d just grabbed Marceline’s jaw out of nowhere, but the siren didn't seem to mind. Her skin was incredibly smooth and slightly cold, a strong contrast to the slightly rough scales of her tail. Bonnibel tried not to move her fingers at all, keeping her hand as still as possible.

The longer this took, the awkward this was going to be. She picked up the tweezers, choosing a random hair and plucking it from Marceline’s scalp. The hair was incredibly long, and Bonnibel had to curl it around so it would fit properly inside the plastic bag. She set that bag aside without closing it, and pulled out another one. She plucked two more hairs as backup samples, storing them in the same bag.

“There. All done.” Bonnibel smiled, shifting back a little. She was ready to get up and put her samples away when Marceline’s eyes opened.

Bonnibel’s train of thought ground to a halt as she stared into Marceline’s eyes. She’d never seen Marceline at this proximity before, and she was enjoying this far too much. Marceline was even more worryingly attractive now, her full attention trained on Bonnibel. There was a strange kind of tension in the air, and Bonnibel wasn’t sure what to do about it.

Was Marceline leaning in? It was subtle, but Bonnibel felt like their faces were getting closer together. Her gaze flickered down to Marceline’s lips, and she wondered if they would taste salty.

Bonnibel barely managed to snap herself out of it at the last second. She leaned back, coughing awkwardly. “Back to the questionnaire!”

She scrambled to her feet, practically throwing herself back into the crate. She sat down, taking a moment to rearrange her hair. She avoided Marceline’s gaze, knowing she probably looked insane now. Why hadn't she pulled away sooner? There was no way Marceline was interested in her like that.

Besides, even if Marceline was hypothetically attracted to Bonnibel, pursuing a relationship like this was still a bad idea. Bonnibel didn't want to be melodramatic, but they literally were different species with completely different lives. It would be difficult to make things work in the first place, let alone continue a functioning relationship. The best course of action was to continue with her study opportunity, and be grateful for that.

“Am I right in saying that you breathe water like a fish? Furthermore, do any other parts of your body require water to maintain themselves?” Bonnibel put on her best clinical voice, resisting the urge to nervously click her pen.

“Yep, I breathe water. I can speak underwater and out on land, but I think my voice carries better down there.” Marceline was back to playing with the tape measurer again, seemingly trying to pull out as much of it as she could. “It kind of hurts when my tail dries out, but it isn’t really an emergency.”

“Alright. You mentioned some dietary restrictions earlier, can you go into that a bit more?” Bonnibel asked, attentively looking at Marceline.

She would be incorporating this information into her study, but it would also be helpful during her next shopping trip. It might be slightly unprofessional, but Bonnibel wanted to buy Marceline more gifts. She just always just keep a record of it under ‘gestures promoting goodwill between the subject and the researcher’ and call it a day.

“Yeah, all of that links back to my species. There are a few sub-categories of siren. I’m not saying this to brag or anything, but mine is pretty rare. I’ve only met a few others like me, and that was a long time ago.” Marceline set the tape measure aside, her expression becoming pensive. “I think the official name is _Desmodus_ , but I might not be remembering that right. Usually I’m just lumped in with the _Abyssals_ , deeper-sea sirens who are more aggressive hunters. Obviously I don’t need to be in the deep sea, but it’s become a kind of catch-all term for some of the loner or scarier sirens.”

Marceline shook her head, seeming to refocus herself. “Basically, I need to consume meat which has a red kind of tint to it. I can’t actually digest anything else, so there’s no point in me eating it. Pink meat is alright too, but I always feel better with I have pure red fish. I was in this area because those fish you were trying to study are a good source of food, and they’re just the perfect—”

Marceline’s stomach growled loudly, cutting her off mid-sentence. However, that wasn’t the part that shocked Bonnibel. Marceline actually blushed, a soft red tint creeping across her cheeks. It was unfairly cute, and Bonnibel desperately wanted to lean in and kiss her cheek to try and make her blush more. She shifted back and forth, forcing herself to continue sitting.

Marceline chuckled awkwardly, resting one hand on her stomach. “Sorry, I’m kind of hungry. I might have skipped breakfast this morning before I came here.”

“Oh, we can continue this later if you’d like. I have to take some measurements for my other research project, and you’ve given me enough to work with for now.” Bonnibel put on a smile, folding up the questionnaire and tucking it into her pocket.

“Okay. See you later, Bonnie.” Marceline rolled over, her tail swishing back and forth as she pushed herself out of the pool. She splashed water everywhere, and Bonnibel quickly picked up the samples and held them up to protect them. Marceline didn't seem to need any help from Bonnibel, and soon enough she was rolling over the edge of the boat.

“Good bye Marceline.” Bonnibel stood up and waved, watching as the dark silhouette disappeared under the water.

She lowered her hand, looking around. The deck looked as messy as she felt, with water and small debris floating everywhere. Bonnibel took a deep breath, setting her samples inside a transparent box and closing it.

Well, at least she could try and regain some of her cool while mopping the deck.


	8. Scintillating Sunsets

**Summary for the Chapter:**

> Marceline and Bonnibel watch the sunset together and y'all get some ~character backstory~

**Notes for the Chapter:**

> It has been a WHILE, huh? I'm so sorry y'all, school just hit me like a sack of bricks and I'm still barely keeping up. I've been struggling a lot with energy and motivation, but I'm still trying to write when I can.
> 
> Thank you to @nebula-gaster for beta reading as usual
> 
> Major thanks to @abadeerly and their wonderful discord server (psst you should message them and join it) for helping me find the motivation to post this!

The sunset was beautiful today. The deep red of the sun radiated outwards, creating a sweeping stroke of orange across the sky. There wasn’t a cloud to be seen, only the bright orange slowly fading out into a faint blue at the edges of the sky. Apart from a few ripples in the waves the sky was reflected perfectly in the water below it, stretching out until the endless horizon was blurred.

Bonnibel propped her chin on her hand, just taking in the view in front of her. She had been working all day, and her brain was exhausted. She couldn't exactly go for a brisk walk to recharge herself, so she settled for staring vacantly at the sunset.

Testing her samples had taken longer than Bonnibel expected, and after that she’d still needed to check in and update her official project. Even though Marceline hadn't come back to continue the questionnaire yesterday, Bonnibel was still plenty tired. She blinked slowly, wondering if she should try and drag herself to bed or just take a quick nap and get back to work.

The decision was made for her when Bonnibel heard a splashing down just off the bow. Marceline swam into view, pulling herself up and squirming until she was sitting on the deck. “Hey.”

“Hello,” Bonnibel mumbled, idly swinging her feet back and forth. Even if she was mentally tired, her body still felt restless.

Marceline didn't try to get any closer to Bonnibel, instead staring out at the sunset. Bonnibel could see Marceline out of the corner of her eye, catching a brief glimpse of shining scales before she forced herself to look back at the sunset. Marceline was as beautiful as she always was, but Bonnibel caught that compliment before it could slip out. She waited silently, unable to think of anything else to say.

Eventually Marceline spoke up, her voice sounding smaller and softer than it usually did. “Can I ask you something?”

Bonnibel closed her eyes, the inside of her eyelids bright red. “Sure, go ahead.”

“Do you have a family? Or even just friends you care about.” Marceline’s tail ran through the water, the soft splashes showing how nervous she was.

A few weeks ago, Bonnibel would have been incredibly suspicious at the question. Why would Marceline need to know anything about her personal life? Was she planning something? Now, however, Bonnibel saw the question in a different light. It seemed like Marceline was feeling lonely, and she wanted to hear about Bonnibel’s bustling social life.

Unfortunately, there wasn't much to tell. Bonnibel took a minute to answer, considering her words carefully. “I have a brother named Neddy. I love him. He’s kind of antisocial though, so we don’t usually spend a lot of time together. I don’t mind it too much though, it’s just how he is. He’s been great about emailing me once I moved out.”

“As for other family… I was raised by my aunt and uncle and they’re nice, but they didn’t really approve of me going to college.” Bonnibel smiled bitterly, recalling the day they had told her she shouldn't come back until she got her “mrs” degree.

Bonnibel had never planned on going to school just to get a husband, but they had never been able to understand that. It was a shame, but Bonnibel had eventually cut all contact with them. In a fast-tracked marine biology major, she couldn't afford any distractions that might bring her grades down.

“I’m doing better in university, but I don’t really have people I would call ‘friends’. I just feel like I never really connect with people, you know? Even when we share common interests, it feels like I’m not quite reaching them or getting as close as others can.” Bonnibel turned to Marceline, noticing that the siren was staring at her intently. “Does that make sense?” She asked, feeling a bit self-conscious. She doubted her rambling was very compelling; she just hoped Marceline wasn't too disappointed with her answer.

“Yeah, it does.” Marceline gave Bonnibel a small smile, but there was a tinge of sadness to her expression.

Bonnibel stiffened as Marceline leaned closer, her eyes widening as Marceline rested her head on Bonnibel’s shoulder. She’d dried out a little bit, so her hair wasn't absolutely soaking wet. She didn't seem to mind Bonnibel’s rigid form, instead snuggling closer.

Was this a dream? Bonnibel wrapped her arm around Marceline, holding the siren close. Her t-shirt was slightly damp, and it certainly felt like Marceline was actually cuddling up to her.

“I’m glad you found me.” Marceline spoke so quietly that for a moment, Bonnibel thought she was hallucinating. “I feel like there’s really something between us, you know?”

“Yes, we’re certainly close,” Bonnibel croaked, her throat feeling tight. She knew Marceline probably wasn't doing this on purpose, but it was still a lot for her to deal with. Pining after the siren from a distance was one thing; watching the sunset together was an entirely different ballpark.

The sun continued to set, and Marceline stayed in Bonnibel’s arms. They sat together in silence, watching the sky darken. Marceline had to lower herself down into the water a few times to keep herself from drying out too much, but Bonnibel didn't mind being soaked in seawater. Even if Marceline was cold, getting to hold her like this made Bonnibel feel very warm.

As a few stars began to appear on the horizon, Bonnibel singled out the brightest one and closed her eyes. It was a silly tradition, but Bonnibel still made a wish. She almost asked if Marceline was familiar with the tradition, but then thought better of it. If she wasn’t, then she might try and get Bonnibel to admit what she’d wished for.

She turned as Marceline pulled away, tilting her head slightly. Sitting in one position for so long meant her back was slightly sore, but she didn't mind it. Was Marceline getting tired of this? Bonnibel tried not to worry yet, looking at Marceline to gauge if anything seemed physically wrong with her.

“Thank you.” Marceline’s icy lips pressed to her cheek, lingering for a few seconds longer than before. Bonnibel closed her eyes, leaning into the embrace. “Good night.”

Before Marceline could pull away, Bonnibel pulled her closer and hugged her tightly. “Good night.” She decided to take a risk, leaning close and kissing Marceline’s cheek.

She pulled back, getting an excellent view of the blush on Marceline’s face before the mermaid pushed off the side of the boat and dove into the water. Bonnibel smiled to herself, waving at the water. She pushed herself up, stretching out her spine as she stood.

Even if she was tired, Bonnibel didn't regret what she’d done. She was happy to comfort Marceline in her time of need, and proud that she could finally get a leg up on flustering Marceline. She might have a different perspective on things in the morning, but for now she felt content. Maybe, just maybe, there was a possibility that she and Marceline could have something deeper than a researcher-subject relationship.


End file.
